DC-DC converters are employed in a variety of applications. DC-DC converters operate by converting an applied DC voltage (usually unregulated) into either a higher or lower regulated DC voltage. DC-DC converters are used in a variety of applications, including power supplies for computers, personal digital assistants, cellular phones and other hand held or portable electronic devices and systems. Each application may have specific demands and performance requirements.
One type of DC-DC converter is a switching converter. Switching converters are often used in portable (e.g., battery powered) devices, as they tend to provide improved efficiency over dissipative conversion methods. In such switched-mode DC-DC converters, an unregulated input voltage is converted into a periodic pulse waveform that has an average value which varies with the ratio of the pulse width to the pulse period. The average value of the pulse waveform may be extracted using filtering techniques, typically including the use of passive filtering components such as capacitors and inductors.
As a practical matter, the use of a high switching frequency in a switched-mode DC-DC converter is desirable because it permits a reduction in the size and weight of the passive filtering components. Switching frequencies in excess of 500 kHz in switched-mode DC-DC converters are common, and the use of large field effect transistors (FETs) as the switching element in the DC-DC converters has facilitated the increase in switching frequency. However, as the switching frequency increases, switching losses during the transition of the switch from “off” to “on” and from “on” to “off” also increase. This is due to the fact that during these transitions, the current passing through the switch and the voltage across the switch both have positive values resulting in a positive voltage-times-current (VI) product, and thus power dissipation. These are known as switch transition losses and are undesirable because they tend to degrade conversion efficiency.